Control device for heating appliance having two operating regimes

ABSTRACT

The control device (25) comprises a thermostat (15) interconnected between a supply source (S) and a heating resistor (4) which comprises two heating elements (41, 42), one of which (42) is supplied only during one of the heating regimes. A temperature limiter (18) is interconnected between the source (S) and the heating element (42). This temperature limiter is sensitive to the heat produced by a resistor (17) having a high resistance value so as to cut-off the supply of said heating element (42) at the time of initial opening of the switch (15a) of the thermostat (15). The device (25) is particularly applicable to electric convectors having a natural convection regime and a blowing regime.

The present invention relates to a control device for a heatingappliance such as a convector with electric heating resistors having twooperating regimes, the first being a natural convection regime and thesecond being an air-blowing regime obtained by means of a blowing unit.

This type of convector is primarily intended for heating premises. Itusually has two operating power levels. Thus the convector is firstemployed at full power in the blowing regime so as to permit a rapidtemperature rise of the premises without any interruption of powersupply and then, when the reference temperature is attained, at lowpower without blowing and in the natural convection regime, thetemperature of the premises being in that case regulated for example bymeans of an electronic on/off thermostat or the like.

The dimensions of the convector of the abovementioned type must be suchthat, in any operating regime, the temperature of its different partswhich are accessible to the user do not exceed maximum permissiblevalues or else values laid down by the manufacturer on the basis of evenmore stringent quality standards.

In electric convectors having two operating regimes which are alreadyknown, one regime is of the forced convection type in which air issucked-in from the exterior of the convector, passes through the heatingresistor and is then blown to the exterior into the premises to beheated. In this design, egress of hot air takes place through one or anumber of outlet grids, the arrangement of which in the upper portion ofthe convector is essentially adapted to operation in the naturalconvection regime.

Investigations made by the present Applicant have in fact shown that,psychologically, users prefer that, in the blowing regime or in otherwords in the forced convection regime in this case, hot air should bedelivered in front of the convector and in the lower portion of thislatter.

As disclosed in patent No. FR-A-2,576,673 in the name of the presentApplicant, there is also known an electric convector having an enclosureforming a convection chimney which has a bottom air delivery opening anda top air delivery opening. The resistance element is placed within theenclosure downstream of the bottom air admission opening. In thisdesign, an impeller is placed within the enclosure in order to extractpart of the hot air formed by natural convection within the convectionchimney and in order to blow part of this air through an additionalhot-air delivery opening formed in the front wall of the enclosure. Aconvector of this type operates in the two regimes aforesaid, changeoverfrom one to the other being carried out manually by the user.

The present invention also has for its object to propose a controldevice for heating appliances of the type aforesaid which permitsautomatic regulation of the operating regimes of these appliances andwhich is of simple design.

In accordance with the invention, the control device for theaforementioned appliance, in which a thermostat is interconnectedbetween the source of supply and the heating resistor comprising twoheating elements, one of which is supplied only during one of theregimes of this appliance, is characterized in that a temperaturelimiter is interconnected between the source and said heating elementwhich is supplied only during one of the regimes of the appliance, thistemperature limiter being sensitive to the heat produced by a resistorhaving a high resistance value so as to cut-off the supply of saidheating element at the time of initial opening of the thermostat switch.

In an alternative embodiment, said control device is characterized inthat a resettable relay is interconnected between the thermostat andsaid heating element which is supplied only during one of the regimes,the coil of said relay being mounted in parallel with said element so asto ensure that the relay opens in order to cut-off the supply of saidelement at the time of initial opening of the thermostat switch.

Thus the combination of a thermostat and temperature limiters or of arelay permits automatic changeover from the blowing regime to thenatural convection regime and on/off regulation in the latter operatingregime.

Moreover, the blowing element is supplied in parallel with the heatingelement which is supplied only in the blowing regime of the heatingappliance.

Other characteristic features and advantages of the invention will alsobe brought out by the description which now follows.

In the accompanying drawings which are given by way of non-limitativeexample :

FIG. 1 is a perspective view of a convector in accordance with theinvention,

FIGS. 2 and 3 are perspective views of said convector, with portionsbroken away, showing the two operating regimes,

FIG. 4 is a schematic longitudinal sectional view showing the interiorof the convector and the air-flow paths in the blowing regime,

FIGS. 5 and 6 are schematic side views with portions broken away showingthe respective end walls of the convector,

FIG. 7 is an electrical diagram of a control device in accordance withthe invention, and

FIG. 8 is an electrical diagram of a control device in an alternativeembodiment of the invention.

In the embodiment of FIGS. 1 to 6, the electric convector includes anenclosure 1 of steel sheet forming a convection chimney, which has abottom opening 2 for the admission of air and a top opening 3 for thedischarge of air. The electric resistor 4 is placed (see FIG. 4) withinthe enclosure 1 directly above the bottom opening 2 for the admission ofair. In practice, this resistor 4 is made up of two heating elements 41,42 which can be supplied separately as will become apparent hereinafter.

The interior of said enclosure 1 contains in addition an impeller 5driven in rotation by a motor 6 so as to extract, in the blowing regime,part of the hot air formed by natural convection within the convectionchimney and so as to blow this air through an additional hot-airdelivery opening 7 (see FIGS. 1 and 4) formed in the enclosure 1.

It is apparent from FIGS. 4 and 5 that the blowing impeller 5 isrotatably mounted within a compartment 8 arranged on one side of theenclosure 1, provision being made in the axis of the impeller 5 for anopening 9 which communicates with the interior of the enclosure 1 whilstthe additional air-blowing opening 7 is provided on one face of saidcompartment 8 which is located opposite to the impeller 5 in the bottomportion of this compartment. Moreover, the impeller 5 is mounted withina housing 11 in the form of a volute, the air outlet 12 of which isdirected towards the bottom wall 13 of the compartment 8 and towards thefront face of this latter in which is formed the opening 7 (see FIG. 5).

In the embodiment illustrated in FIGS. 3 and 4, the compartment 8 isprovided in the vicinity of its bottom wall 13 with a second opening 14which communicates with the interior of the enclosure 1 opposite to theheating resistor 4. As will be brought out in greater detail in thedescription of operation, this opening 14 serves in the blowing regime,to reinject part of the air drawn from the compartment 8 by the impeller5, into the enclosure 1 on the heating elements 41, 42. The opening 14is smaller in crosssection than the additional air delivery opening 7.

With reference to FIGS. 7 and 8, the control device 25 includes athermostat 15 for adjusting the reference temperature. The thermostat 15is placed (FIG. 4) within the compartment 8 in a region which is notaffected by the hot air stream blown by the impeller 5, for examplebehind the volute 11. One of the terminals A of the switch 15a of thethermostat 15 is connected to the electric supply source S of theconvector whilst its other terminal B is connected to one of theterminals of the heating element 41 which is intended to be suppliedboth in the natural convection regime and in the blowing regime. Theother terminal of the heating element 41 is connected to the source S.

In FIG. 7, a temperature limiter 18 such as a thermal switch, forexample, is interconnected between the source S and one of the terminalsD of the heating element 42 which is intended to be supplied only in theblowing regime. The limiter 18 is designed and arranged within thecircuit of the control device 25 so as to be sensitive to the heatproduced by a heating resistor 17 having a high value of resistance, forexample a value within the range of 16 to 20 k , in order to open whenthis heating resistor is supplied and thus to cut-off the normal supplyof the heating element 42.

The heating resistor 17 is mounted in series with a second temperaturelimiter 16 between that terminal D of the limiter 18 which is connectedto the heating element 42 and the terminal B of the switch 15a. Thistemperature limiter 16 is also designed and arranged within the circuitof the device 25 so as to be sensitive to the heat produced by theheating resistor 17 and to open when said heating resistor is supplied.It will preferably be ensured that the limiter 16 opens substantially atthe same time as the limiter 18.

Moreover, the motor 6 of the impeller 5 is mounted in parallel with theheating element 42 between the terminal D and the source S. A switch 21interconnected between the source S and the terminal A permits turn-onor turn-off of the convector.

The heating element 41 preferably has a power of 1000 W whilst theelement 42 has a power of 500 W or 1000 W in order to obtain a totalpower of 1500 or 2000 W in the blowing regime.

The control device 25 is preferably placed within the compartment 8opposite to the external control elements 10 of the convector.

The operation is as follows :

The thermostat 15 having been set at its reference temperature such as20° C., for example, and the convector being connected to the source S,the switch 21 is then placed in the closed position whilst the switch15a of the thermostat 15 is also closed. The temperature limiters 16, 18are closed since they are not subjected to any temperature rise, theheating resistor 17 being shunted by the portions of circuit AB and AD.The points of connection A and C are enabled and the heating elements 41and 42 as well as the motor 6 of the impeller 5 are supplied withcurrent.

In this blowing regime of the convector, the air streams are oriented asrepresented by the arrows in FIG. 3. An air stream E enters theenclosure 1 through the bottom opening 2, passes through the heatingelements 41 and 42 and rises within the convection chimney of theenclosure 1. A portion C of the hot air stream E is evacuated to theexterior through the top outlet 3 whilst the other portion A is drawninto the compartment 8 through the opening 9 under the action of theimpeller 5 and is discharged by this latter towards the bottom wall 13of the compartment 8. Under these conditions, a portion S of the streamA is discharged to the exterior through the opening 7 at a distance fromthe opening 2 and with an orientation with respect to said opening 2which prevents it from returning into the enclosure 1 through saidopening whilst the other portion R is reinjected through the opening 14into the enclosure 1 on the heating elements 41 and 42.

Tests performed by the present Applicant have shown that the stream Rrepresents ten to twenty per cent of the stream A whilst the stream Cwhich passes out of the enclosure 1 through the opening 3 is higher byfifteen to twenty-five per cent than the stream which would pass out ofsaid opening 3 in the absence of the opening 14. The difference of fiveper cent with respect to the ratio A/R is justified a priori by theincrease in velocity of the airflow within the convection chimney as aresult of a reduction in overall pressure drops. By virtue of relativecooling of the heating elements 41 and 42 and efficient stirring of theairflow within the convection chimney by the stream R, the meantemperature of the stream C is reduced, thereby correlatively coolingthe walls of the enclosure 1 and the grids which partially close the airoutlet 3. Moreover, the hot air stream S blown through the outlet 7provides a very distinct improvement in heating comfort since themajority of users highly appreciate blowing of hot air in the lowerportion and on the front face of the convector.

When the temperature of the room comes close to the referencetemperature (for example 20° C.), the switch 15a of the thermostat 15opens the circuit ABC. Taking into account the high value of resistanceof the heating resistor 17, a current of low intensity then circulateswithin the circuit which connects in series the source S, the heatingresistor 17 and the element 41. This current of low intensity heats-upthe heating resistor 17 to a sufficient extent to open the limiters 16and 18. Thus the elements 41 and 42 no longer generate heat and theimpeller 5 no longer operates.

When the temperature of the room falls below the reference temperature,the switch 15a of the thermostat 15 again closes, with the result thatthe element 41 is again supplied at its maximum intensity and heatsupagain. Since the limiters 16 and 18 are still in the open position, theelement 42 does not generate any heat and the impeller 5 still does notoperate.

Thus the control device 25 in accordance with the invention ensureson/off regulation in the natural convection regime. At any moment, thelimiters 16 and 18 may be reclosed, with the result that the convectoragain operates in the cycle described in the foregoing which begins withthe air-blowing regime.

In FIG. 8 which illustrates an alternative embodiment of the controldevice 25, the terminals of the circuit of said device 25 are designatedby the same letters as in FIG. 7. A relay 20 which can be reset by aresetting push-button 30 is interconnected between the terminals B and Dof the circuit of the device 25. The relay 20 is maintained in theclosed position after engagement of the push-button 30 by supplying therelay coil 22 which is mounted in parallel with the terminals D and C.

The operation is as follows :

when the thermostat 15 has been set at its reference temperature and theconvector has been connected to the source S, the switch 21 and therelay 20 are then placed in the closed position whilst the switch 15a ofthe thermostat 15 is also closed. The connection points A, B, C and Dare under tension and the heating elements 41 and 42 as well as themotor 6 of the impeller 5 are supplied with current. The convector thenoperates in the blowing regime.

When the temperature of the room comes close to the referencetemperature, the thermostatic switch 15a opens the circuit ABC, with theresult that the coil 22 is no longer supplied. The contact 31 of therelay 20 then opens, with the result that the elements 41 and 42 nolonger heat-up and the impeller 5 no longer operates.

When the temperature of the room falls below the reference temperature,the switch 15a again closes, with the result that the element 41 againbegins to heat-up. Since the coil 22 is still not supplied, the relay 20remains closed, with the result that the element 42 does not heat-up andthat the impeller 5 does not operate either. At the following turn-on ofthe convector, if the relay 20 is reset, the convector again operates inaccordance with the above-described cycle which starts with the blowingregime.

By virtue of a particularly simple design, the control device 25 whichhas just been described thus ensures automatic changeover from theblowing regime to the on/off regulated natural convection regime.

As will be readily apparent, the control device which has just beendescribed is applicable to any electric heating appliance having twoheating regimes.

We claim:
 1. Control device for electric heating apparatus, comprisingtwo heating resistors (41, 42), a supply source (S) for said heatingresistors, a thermostat (15a) having two terminals (A, B), one of saidterminals being connected to said supply source (S) and the other saidterminal (B) being connected to one (41) of said heating resistors, afirst temperature limiter (18) having two terminals, one of saidterminals being connected to said supply source (S) and the other saidterminal (D) being connected to the other said heating resistor (42), athird heating resistor (17) being connected between said other terminal(B) of the thermostat (15a) and said other terminal of said firsttemperature limiter (18), a second temperature limiter (16) beingconnected between said third resistor (17) and said other terminal (B)of the thermostat (15a), said two temperature limiters (16, 18) beingresettable in closed position and being sensitive to the heat of saidthird resistor (17) when it is traversed by a current, said thirdresistor (17) having an ohmic value such that said third resistor (17)is traversed by a negligible current when said thermostat (15a) isclosed, and when said thermostat is open to heat said temperaturelimiters (16, 18) to open said limiters and cut-off the supply of saidtwo heating resistors (41, 42).
 2. Control device for electric heatingapparatus, comprising two heating resistors (41, 42), a supply source(S) for said heating resistors, a thermostat (15a) having two terminals(A, B), one of said terminals being connected to said supply source (S)and the other said terminal (B) being connected to one (41) of saidheating resistors, a relay (20) that can be reset by a resetting button(30), said relay being interconnected between said other terminal (B)and said other heating resistor (42), said relay (20) having a relaycoil (22) connected in parallel with said other heating resistor (42),said relay coil (22) maintaining said relay in closed position when itis supplied with current.